While a considerable amount is known about genetic influences in alcoholism, relatively little is known about genetic influences in other type of drug abuse. It has not been conclusively demonstrated, for example, if genetic influences are involved in other drug abuse, or whether the genetic involvement is the same as that for alcoholism. In 1992, Dr. Svikis at Johns Hopkins University and co investigators (including NIDA intramural researchers) initiated a twin study of drug abuse. Drug abusing twins were recruited from several Baltimore based drug treatment and research facilities. Identical (monozygotic) and non identical (dizygotic) twin participants were asked to complete a questionnaire with detailed information on nature and extent of cigarette, alcohol and drug use in themselves and their family members. At the time of the study's three year renewal (1995), information had been obtained on a total of 107 twin probands. At that time, Dr M van den Bree became PI on the project, and since that time 7 additional twin probands have been recruited for the study. In addition, the protocol was expanded to include obtaining a blood sample from twins for future molecular analysis of relations between drug use and genetic markers. Twin recruitment is expected to continue for the next several years.